Field-effect viewing storage tube

ABSTRACT

An improved halftone charge-controlled viewing storage tube which uses the field-effect principle is described. The tube is characterized as having as its face plate a panel comprising a light transparent support plate, a light transparent conductive coating on one side of such support plate a first electroluminescent material layer disposed over the conductive coating and a layer of a uniform mixture of a second electroluminescent material and a photoconductor is disposed over the first electroluminescent layer. The first electroluminescent material is selected to emit light in the visible range of the electromagnetic spectrum, while the second electroluminescent material is sealed to emit light in the near ultraviolet region of the electromagnetic spectrum. Large panels 12 X 12 inches and larger can be used to give sharp clear images. Additionally, high writing speed is obtained in the storage tube. Information can be stored or can be disposed without being stored. Also, the storage tube is capable of providing long viewing times.

United States Patent Primary ExaminerRodney D. Bennett. Jr. Assistant ExaminerJ. M. Potenza Attorneys-Haniiin and Jancin and Hansel L. McGee ABSTRACT: An improved halftone charge-controlled viewing storage tube which uses the field-effect principle is described. The tube is characterized as having as its face plate a panel comprising a light transparent support plate, a light transparent conductive coating on one side of such support plate a first electroluminescent material layer disposed over the conductive coating and a layer of a uniform mixture of a second electroluminescent material and a photoconductor is disposed over the first electroluminescent layer. The first electroluminescent material is selected to emit light in the visible range of the electromagnetic spectrum, while the second cloctroluminescent material is sealed to emit light in the near ultraviolet region of the electromagnetic spectrum.

Large panels 12 X 12 inches and larger can be used to give sharp clear images. Additionally, high writing speed is obtained in the storage tube. Information can be stored or can be disposed without being stored. Also, the storage tube is capable of providing long viewing times.

PATENTED SEP28 IHYI FIG.1

FIG. 2

wi l

INVENTORS EUVAL S. BARREKETTE HERBERT B. BASKIN ATTOR Y FIELD-EFFECT VIEWING STORAGE TUBE BACKGROUND oF THE INVENTION 1. Field of the Invention This invention relates to an improved halftone charge-controlled viewing storage tube.

2. Description of the Prior Art In the past, solid-state image panel intensifiers have been developed which can convert an input optical image to a stored luminescent image. Most of these employ as active layers, an electroluminescent powder layer for creating the output image and a photoconductive layer whose impedance is locally varied by the input light radiation. In one type of panel, image storage for a limited time is possible because of slow decay of conductivity of the photoconductive layer following exposure to an optical image. In another type of panel, optical feed back is employed at each picture element. When the impedance of the photoconductive control element is lowered by the input light, a portion of the output light from the corresponding phosphor element excites the photoconductor, thus maintaining the element in the On condition after cutoff of the input. A third type of storage panel employs a special type of photoconductive control layer of Cd Se which exhibits a hysteresis efiect. In this case the photoconductor is triggered to a higher level of conductivity by the input light remaining in this condition more or less indefinitely until the supply voltage is cut off.

More recently, improved image storage panels have been developed using the principle of field-efiect controlled conductivity. These panels employ an electroluminescent powder layer for generation of the output image and a ZnO powder layer for control and storage purposes. The exposed ZnO surface is uniformly charged to a potential to reduce its conductivity and erase old information. Following this the panel is exposed to an optical image which discharges local areas, producing a stored charge pattern on the ZnO surface. The charge pattern produces a conductivity pattern in the ZnO layer which controls the luminescent output of corresponding areas of the adjacent phosphor layer. Panels of this type are described in the publication to Benjamin Kazan, entitled Image-Storage Panels Based on Field-Effect Control of Conductivity Proceedings of the IEEE, Volume 56, Number 3, Mar. 1968.

Storage panels of the above types have a variety of limitations. Paramount among these limitations is the need for using optical imaging of the photoconductive layer, i.e., passing of light through a transparency to thereby impose an image on the photoconducto'r layer. These panels are not capable of receiving information electronically, as from a computer, and subsequently transmitting this information.

Other limitations of the above prior art display panels, include restricted output brightness, limited viewing time due to the photoconductive decay process and the inability to store halftones because of the bistable nature of such panels.

An improved field-effect image storage tube is described in the publication to Benjamin Kazan and .I. S. Winslow, entitled Viewing Storage Tubes Based upon F ield-Effect Conductivity Control," Proceedings of the IEEE, Volume 56, Number 10, pp. 1716-1717, Oct. 1968. The image storage tube described in the above is an improvement over other like prior art devices. However, the device requires a collector grid which operates admirably where the panel member is about 2-3 inches square. However, where large panels are desired the collector grid becomes impractical and diffuse images are formed.

SUMMARY OF THE INVENTION According to an aspect of this invention, an improved image storage tube is provided with a display panel whose operation is based on the principle of field-effect conductivity control described in the above-mentioned publications to Benjamin Kazan, et al. The improved image storage tube of'this inven tion is characterized by having a display panel member as its faceplate comprising a light transparent insulating support member having coated on one of its surfaces film strips of light transparent conductive material, such as, tin oxide. Disposed on the transparent conductive material is a first electroluminescent material which emits light in the visible range of the electromagnetic spectrum. Finally, a layer of a uniform mixture of a photoconductive material and a second electroluminescent material is disposed on said first electroluminescent material. Alternately the photoconductive material and the second electroluminescent material may be present in separate layers with the second electroluminescent material being contiguous with the first electroluminescent material and the photoconductive material being disposed thereon. Images on the above panels are erased by flooding with electrons and are written upon by high energy electron beams.

The above described panel member can be made as large as 12Xl2 inches and is adapted to electronically receiving and storing images at high speeds. The images displayed are sharp and clear.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a portion of the cross section of the panel of this invention. The figure depicts a glass plate whose surface is provided with a set of fine transparent conducting film strips. Alternate lines are connected together to form an interdigital system with AC voltage being applied across the two sets of lines. The sandwich structure is coated on the surface of the glass plate.

FIG. 2 is a portion of the cross section of an alternate panel structure to FIG. 1. The figure shows the two electroluminescent materials being contiguous with each other, with a layer of the photoconductive material being disposed on the second electroluminescent material.

FIG. 3 is a side sectional view of the embodiment of the storage tube of the present invention showing the internal structure of the storage target together with an electron flood gun and a high-voltage electron beam writing gun.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. I, one embodiment of the image storage panel or target 10 includes a light transparent support plate 12 of glass or other insulating material having film strips of light transparent conductive coating 14 of tin oxide or other similar material applied to one side of such support plate in a conventional manner. The support plate 12 is coated with about 50 lines per inch of the conductive film strips 14. An electroluminescent (EL) material is provided on the support plate 12 over the conductive film strip 14 to function as a viewing screen 16. The EL material layer in screen 16 is uniformly distributed over the support plate 12 in the form of a thin film of about 1 to 2 mils thick. The material used in screen 16 is one that emits light in the visible range of the electromagnetic spectrum. For example, phosphors such as the P-1 and P-3l types which emit substantially yellow green light, or the P-l I- type phosphor which emits a blue light, or P-22-type phosphor which emits red light can be used. Uniformly dispersed on screen 16 is a photoconductive layer 18 of a uniform mixture of a photoconductive material and a second EL material. Layer 18 is a thin film of about I mil or less. The photoconductive material in layer 18 serves to receive and store an image when it is charged from light emitted from the second EL material which is uniformly dispersed therein. The second EL material is selected from materials which have good light efficiency in the near ultraviolet range of the electromagnetic spectrum. In preferred embodiments of the invention, a phosphor material such as the P-l6 type, which generally emits light having a wavelength of less than 4,000A., e.g., in the range of 3,500A. to 4,000A., is used. The photoconductive material is selected from materials such as polyvinyl carbazoles, chalcogenides such as Cd Se, ZnO and the like. In preferred embodiments of the invention ZnO is used.

The transparent conductive film strips 14 are connected to a set of fine conducting alternate leads 20 and 22. Leads 20 and 22 are connected to form an interdigital system with AC voltage of about 6 kv. from source 24 (See FIG. 3) being applied across the lines 20 and 22. Leads 20 and 22 extend through a seal between glass support 12 and a ceramic funnel member 26 which, together, form the envelope of cathode-ray tube 28 with such support plate 12 providing the faceplate of tube 28. Leads 20 and 22 serve to supply current to conductive film strips 14. Current from such leads flow between conductive film strips 14 through screen layer 16, across the layer 18 and back through the layer 16 of the adjacent conductive coating 14. The paths of the current flow are shown by the dashed arrows in FIG. 1. The AC voltage appears across portions of layer 16 and causes it to emit a light pattern.

Positioned in cathode-ray tube 28 are flood gun 30 and writing gun 32. Flood gun 30 serves to flood the faceplate (shown in FIG 3) generally as 34, with electrons, until a uniform charge is obtained on the layer 18. An ()ff-On switch 36 is attached to flood gun 30 to control the flow of electrons therefrom. Writing gun 32 provides a beam of high-velocity electrons which is deflected in a conventional manner by suitable electrostatic or electromagnetic deflection means 38 provided as part of such gun.

in operation, a negative charge is applied to layer 18 by positioning switch 36 in the On position of the negative pole of power source 40 causing the flood gun 30 to emit electrons having a potential of about 6 kv. The emitted electrons apply a uniform charge to layer 18 thereby reducing the conductivity of the photoconductive material in said layer 18 without appreciably affecting the electroluminescent material therein. As a result of uniformly charging layer 18, a former image that may have been stored therein is erased. Subsequent to the charging step an image is imposed on layer 18 by a highvelocity electron beam, having a potential of -12 kv. or higher, emitted from writing gun 32. The emitted electron beam causes the electroluminescent material in layer 18, in the region penetrated by said electron beam, to emit light having an input radiation of approximately 1 microjoule/cm. and having wavelengths of the order of 4,000A. or less. This emitted light produces a stored charge pattern in the photoconductive material.

When an AC voltage of about 400 volts at a frequency of 1 kHz. is applied from source 24 across the light transparent conductive film strips 14 via conductive lines 20 and 22, an electric field occurs, according to the stored pattern, across layers 16 and 18, as shown by the dashed arrows in FIG. 1, thereby resulting in a visible image. The stored images have a brightness as high as 20 foot-lamberts and a maximum contrast of about 100:1 and exhibit good halftones. Although a halftone image can be retained for periods of the order of an hour or more, it can be rapidly erased when desired by recharging layer 18 to a uniform negative potential.

Where the alternate panel member shown in FIG. 2 is substituted for that of FIG. 1, an image is produced similarly to the operation described above. When this panel is used, photoconductive layer 19 is negatively charged by flood gun 30 as above. Writing is also accomplished as above except that the electrons from writing gun 32 penetrate layer 19 to cause near ultraviolet light emission from the electroluminescent layer 17 which emits light in all directions. Light emitted in the direction of layer 19 causes a charged pattern to be developed therein. It should be noted that light emission in the direction of electroluminescent material 16 has no effect thereon. As above, when an AC voltage is applied to light transparent lines 14, an electric field is effected across layers 16, 17 and 19 to produce a visible image as above. The image so produced has the same good qualities as is described above.

What is claimed is:

1. An improved viewing storage tube having field-effect conductivity control including combined direct viewing storage target and electroluminescent screen, comprising:

a. a support member of light transparent insulating material;

b. a screen of a first electroluminescent material supported on one side of said li ht transparent support member; c. an image storage ayer disposed on said screen, said image storage layer being composed of a uniform mixture of a photoconductive material and a second electroluminescent material, having a light emission different from said first electroluminescent material, to receive and store an image electronically imposed thereon; and

d. a conductive layer supported on one side of said support member to establish an electric field in the presence of an AC potential, across said screen and said image storage layer whereby the image stored in said image storage layer is displayed on said screen.

2. An improved viewing storage tube according to claim 1 in which the conductive layer is a light transparent conductive film contiguous with the surface of the support member.

3. An improved viewing storage tube according to claim 1 wherein said first electroluminescent material emits light in the visible region of the electromagnetic spectrum and said second electroluminescent emits light in the near ultraviolet region of electromagnetic spectrum.

4. An improved viewing storage tube according to claim 1 which also includes:

means for producing a writing beam of high-velocity electrons and moving said writing beam across said image storage layer to form an electron image thereon; and

means for flooding said image storage layer with low velocity electrons to erase an image stored in said storage layer.

5. An improved viewing storage tube having a field-effect conductivity control including combined direct viewing storage target and electroluminescent screen, comprising:

a. a support member of light transparent insulating material;

b. a screen of a first electroluminescent material supported on one side of said light transparent support member;

c. a layer of a second electroluminescent material contiguous with said screen, said second electroluminescent material having a light emission different from said first electroluminescent material;

d. a photoconductive layer contiguous with said layer of said second electroluminescent material, said photoconductive layer being receptive to and capable of storing an image electronically imposed thereon; and

e. a conductive layer supported on one side of said support member to establish an electric field, in the presence of an AC potential, across said screen and said photoconductive 6 layer.

6. An improved viewing storage tube according to claim 5 in which the conductive layer is a light transparent conductive film contiguous with the surface of said support member.

7. An improved viewing storage tube according to claim 5 wherein said first electroluminescent material emits light in the visible region of the electromagnetic spectrum and said second electroluminescent material emits light in the near ultraviolet region of the electromagnetic spectrum.

8. An improved viewing storage tube according to claim 5 which also includes:

means for producing a writing beam of high-velocity electrons and moving said writing beam across said image storage layer to form an electron image thereon; and

means for flooding said image storage layer with lowvelocity electrons to erase an image stored in said image storage layer. 

2. An improved viewing storage tube according to claim 1 in which the conductive layer is a light transparent conductive film contiguous with the surface of the support member.
 3. An improved viewing storage tube according to claim 1 wherein said first electroluminescent material emits light in the visible region of the electromagnetic spectrum and said second electroluminescent emits light in the near ultraviolet region of electromagnetic spectrum.
 4. An improved viewing storage tube according to claim 1 which also includes: means for producing a writing beam of high-velocity electrons and moving said writing beam across said image storage layer to form an electron image thereon; and means for flooding said image storage layer with low velocity electrons to erase an image stored in said storage layer.
 5. An improved viewing storage tube having a field-effect conductivity control including combined direct viewing storage target and electroluminescent screen, comprising: a. a support member of light transparent insulating material; b. a screen of a first electroluminescent material supported on one side of said light transparent support member; c. a layer of a second electroluminescent material contiguous with said screen, said second electroluminescent material having a light emission different from said first electroluminescent material; d. a photoconductive layer contiguous with said layer of said second electroluminescent material, said photoconductive layer being receptive to and capable of storing an image electronically imposed thereon; and e. a conductive layer supported on one side of said support member to establish an electric field, in the presence of an AC potential, across said screen and said photoconductive layer.
 6. An improved viewing storage tube according to claim 5 in which the conductive layer is a light transparent conductive film contiguous with the surface of said support member.
 7. An improved viewing storage tube according to claim 5 wherein said first electroluminescent material emits light in the visible region of the electromagnetic spectrum and said second electroluminescent material emits light in the near ultraviolet region of the electromagnetic spectrum.
 8. An improved viewing storage tube according to claim 5 which also includes: means for producing a writing beam of high-velocity electrons and moving said writing beam across said image storage layer to form an electron image thereon; and means for flooding said image storage layer with low-velocity electrons to erase an image stored in said image storage layer. 